1. Field of Invention
This invention relates to tripod joints and more particularly to external members for tripod joints and method for manufacturing same.
2. Prior Art
Referring to FIG. 1, shown therein is a non-extensible high joint angular tripod type tripod joint of the prior art. As shown in FIG. 1, the tripod joint includes an external member 1. The external member 1 includes a cup shaped spider holding portion 2 and a stem portion 3 integrally connected to the bottom of the spider holding portion 2. The stem portion 3 is formed with splines for transmitting power.
In the spider holding portion 2, a spider 6 is integrally formed with trunnions 5 projecting in three directions. The trunnions 5 engage with projection 7 formed on the inner surface of the spider holding portion 2 and thereby support the spider 6. The trunnions 5 are each axially slydably and rotatably coupled to roller 8. The rollers 8 roll in rolling grooves 10 of tulip shaft 9. The rollers 8 are coupled to the tulip shaft 9 such that rotating force can be transmitted even if the tulip shaft 9 and the external member 1 make an angle that is less than a predetermined value. A tripod spring 11 supports the tulip shaft 9 on the spider 6 and a poppet 12 is coupled to the end face of the spider 6 opposite to the tripod spring 11 and is urged by a compression spring 13 in a direction opposite to the tripod spring 11.
In this conventional external member 1, the spider holding portion 2 and the stem portion 3 are arc welded together to form the external member 1. In the case of arc welding, as shown in FIG. 2 for example, a flange 3A of the stem portion 3 is inserted into and welded to a large hole provided in the bottom 2B of the cup shaped spider holding portion 2.
However, in the case of arc welding, there have been such disadvantages that weld beads B, weld spatters and other deposits result on the inside of the spider holding portion 2 and their removal thereof is troublesome. Also, a large variation in bead shape results and the quality of the product is not uniform. Therefore welded external members 1 must be inspected periodically by cutting the product into sections and frequently it is not always possible to set the tripod spring 11 stably on the weld beads B having a large variation in shape when the tulip shaft 9 is assembled.
In an attempt to overcome these disadvantages, another form of external member 1 as shown in FIG. 3 has been developed.
In FIG. 3, the flange 3A formed on a stem portion 3 is friction welded to the end face of a cylindrical member 2A thereby forming the bottom of an external member 1. In the case of friction welding described above, as indicated by the reference 14 in the drawing, internal weld flash is formed inside of the external member 1. The weld flash 14 is firmly secured to the cylindrical member 2A and the flange 3A. Moreover, there are many small pieces of burrs 14A and 14B which are caught at the tips of the flash or small pieces of burrs 14C caught in the center dent of the flash formed on two sides of the flange 3A and the cylindrical member 2A in such a manner that the small caught pieces of burrs may easily fall off.
Since the amount of welding is usually set at a small value in order to prevent heat distortion and changes in the structure caused by heat treatment due to friction welding, the internal weld flash 14 radiates heat easily through heat conduction and upon completion of the welding undergoes a sharp decrease in temperature and hardens very fast. It is therefore extremely difficult to machine these hardened weld flash 14 and considerable labor and a very high cost is required to anneal them by an electric arc or flame from the inside. Even after the machining, the inside of the spider holding portion 2 must be cleansed. The cleansing treatment, including dehydrating and drying of the holding portion 2, is considerably troublesome and expensive.
Since it is so difficult to machine only the small pieces of burrs with a turning lathe or the like leaving the hardened internal weld flash 14 intact, other methods such as wire brushing, shot blasting, high speed water streams or the like have been utilized to remove the small pieces of burrs and by such methods it is almost impossible to completely remove the small pieces of burrs on the internal weld flash in a short period of time. Accordingly, such universal joints have heretofore been used as finished products that have small pieces of burrs remaining thereon which have not come off even after the removal work and include small pieces of broken wire brush or crushed small pieces of shock balls, etc. which result from the attempted removal process. These small pieces of material have created a disadvantage in that these small pieces frequently break off and cruch into between the rollers and roll grooves of the tulip shaft and cause problems.
Heretofore, there has neither been manufactured an external member, wherein a stem portion of a non-extensible tripod joint for a large angle is frictionally welded to a cup-shaped member, nor found a literature known in the art. Because the cup-shaped member in the tripod joint is made of a very thin sheet material as compared with that of the Birfield, joint such a method has been proved unsuccessful that which is inferred from the frictional welding technique of the Birfield joint having a cup-shaped member of large thickness. More, specifically there have been problems that, in general, in the case of a cup-shaped member made of a thin sheet of material, control of the conditions for frictional welding becomes difficult due to the high pressure gas confined in a space formed by the stem and the cup-shaped member, and further, a deformation is caused at the bottom of the cup-shaped member, which is bulged inwardly to the interior of the cup.